group (chemistry)

In chemistry, a vertical column of elements in the periodic table. Elements in a group have similar physical and chemical properties; for example, the group I elements (the alkali metals: lithium, sodium, potassium, rubidium, caesium, and francium) are all highly reactive metals that form univalent ions. There is a gradation of properties down any group: in group I, melting and boiling points decrease, and density and reactivity increase.

Group 0 consists of the noble gases (rare gases) and group II consists of the alkaline-earth metals. Those elements placed between group II and III are the transition metals and group VII contains the halogens.